The present invention relates to an improved thermally conductive composite gasket for an internal combustion engine having improved strength characteristics and variable thickness.
A thermally conductive gasket having high strength, particularly in the radial direction, is essential in heavy duty applications. It has been proposed in the past to bond a facing layer to both faces of a heavy gauge solid metal shell. The metal shell provides strength while the facing layer facilitates the conformability of the gasket to its mating surfaces. Unfortunately, it has been difficult to practically achieve a gasket having a metal layer bonded to a facing layer. Under high loads, portions of the facing layer may begin to separate or slide relative to the metal shell.
There are manufacturing difficulties in bonding a solid metal core to a facing layer. Typically, a thermosetting adhesive is required for the bonding process. A thermosetting adhesive has the advantage of being able to withstand high temperatures such as those experienced within internal combustion engines. However, when a thermosetting adhesive is initially set, gases are generated, particularly from the adhesive itself. The generated gases are unable to escape and blistering of the facing layer typically results, reducing the effectiveness of the gasket.
Further, the bonding process must be carefully controlled or areas of reduced bonding may occur. In addition, the various layers may become misaligned during bonding. In particular, tracking can become a problem when hot rollers are used to cure the adhesive. Finally, during assembly, the facing layers may become curled, reducing the area of contact with the adhesive and complicating assembly operations. For example, arcing may occur if a curled facing layer comes into contact with an element of a preheating induction unit, vaporizing a portion of the adhesive.